In the production of product labels, it is often desirable to print the labels in vivid, multi-color patterns that require high quality, multi-color printing systems. For example, a multi-color label printing system may comprise six or more printing stations. Each of the printing stations applies a printing ink in a single color (which may be a primary printing color or a special color blend) to a web of the paper stock. The printing inks applied by the plurality of printing stations collectively form a repetitive, multi-color label pattern on the web of paper stock.
In high quality, multi-color, label printing systems, it is known to dry each color printing ink after it is applied to the web, so that another color printing ink can be applied to the web without distorting the pattern of the ink applied at the earlier print stations. In order to dry the printing inks, it is known to direct the web through an oven or a curing station after each printing station. For example, if the different color printing inks used in the printing system are ultraviolet (UV) curable, the web of label stock is directed through a UV curing station after printing ink is applied at each of the printing stations.
It is known to apply a top protective finish coating to the printed label stock after the web of label stock has been printed (and the printing inks dried in the manner described above). The finish coating gives the printed label stock a desired finish, protects the printed label stock from damage or deterioration from ambient conditions, (e.g., moisture, sunlight, etc.), and resists scratching or abrasion of the printed label stock.
One known technique for applying a top, protective finish coating to printed label stock is to laminate a film of a transparent, protective material to a web of printed label stock. For example, it is known to superimpose a transparent film of a material such as Mylar.RTM. onto a web of printed label stock to form a laminate, and then heat cure the laminate, to fix the Mylar.RTM. film to the printed label stock. Also, it is known that some types of Mylar.RTM. film have pressure sensitive adhesive coated on one side thereof. Such types of Mylar.RTM. film can be laminated to a web of printed label stock by pressing the adhesive coated side of the Mylar.RTM. film against the web of printed label stock.
Applicants believe that laminating a Mylar.RTM. film to printed label stock is a relatively expensive way to apply a finish coating to the label stock, principally because Mylar.RTM. film is a relatively expensive material. Moreover, in order to change the thickness of the finish coating, it would be necessary to change the thickness of the Mylar.RTM. film which is laminated to the web of printed label stock. Thus, a label manufacturer would have to warehouse Mylar.RTM. film in as many different thicknesses as may be required (and as are available) to enable the label manufacturer to change the thickness of the film laminate. If Mylar.RTM. film is unavailable in certain desired thicknesses, that may be a significant limitation on a label manufacturer's flexibility to produce finish coatings in such thicknesses. Also, since the thickness of Mylar.RTM. film coated with pressure sensitive adhesive is affected by the thickness of the pressure sensitive adhesive, that may be another limitation on a label manufacturer's flexibility to produce finish coatings in different thicknesses. Thus, a label making system in which a Mylar.RTM. film laminate is used as a finish coating is not believed to be particularly flexible when it comes to adjusting the thickness of the finish coating. Furthermore, the equipment required for laminating a film of Mylar.RTM. to a web of printed label stock would be located primarily in the processing area of a label making plant, and that is a significant factor which would have to be taken into account in formulating a layout for the processing area of a label making plant.
Another known technique for applying a finish coating to a web of label stock is to apply a coating of radiation curable varnish, for example, ultraviolet ("UV") curable varnish, to the label stock, and to cure the varnish at a curing station. Moreover, since multi-color label printing systems are generally configured to dry the web after ink is applied at each printing station, it is known to use one of the printing stations to apply the UV curable varnish to the web of printed label stock, and then to direct the web through a UV curing station. If the printing system uses UV curable printing inks, the UV curing station may be the same curing station used for curing the printing inks.
Applicants believe that a label-making system utilizing a UV curable varnish as a finish coating has its own drawbacks. For example, applicants believe that curing time may be a drawback, because certain types of UV curable varnishes require significant amounts of curing time, in order to harden the varnishes. Moreover, some UV varnish curing systems generally require special venting system(s) for exhausting vapors and fumes associated with the removal of volatile solvents from the varnish during curing. Also, when a UV curable varnish is applied by one of the printing stations of a multi-color printing system, the system necessarily loses some of its color printing capabilities. That can be a significant problem, where a label maker requires the full use of a multi-color printing system to print a particular manufacturer's labels.